Flameproof screen for use in airconditioning conduits



Mar'ch 18, 1 947. 4, FORD 2,417,408

FLAME-PROOF SCREEN FOR USE IN AIR CONDITIONING CONDUITS Filed Nov. 26, 1942 2 sheets-sheet 1 1s 12 1 e 11 4 7 5 11 A Y k I 1 1 1- 1 1 1 1 FIG. 2

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INVENTOR 1 Jbhn W. Ford Patented Mar. 18, 1947 UNITED STATES PATENT ornce FLAMEPROOF SCREEN FOR USE IN AIR- CONDITIONING CONDUITS M John W. Ford, Silver Spring, Md. Application November 26, 1942, Serial No. 467,067

4 Claims. (01. 98-533) (Granted under the act of March 3, 1883, as.

amended April 30, 1928; 370 O. G. 757) This invention relates 'to Ventilating and air conditioning conduit circuits and more particularly to arrangements used therein whereby to make them safe against accidental ignitionof the gases where combustible ingredients might be present in the gaseous mediums that are being circulated.

In the conventional flame proof screen, the object is to cool the air stream, to prevent flame propagation, by a series of plates which conduct the heat away from the air stream, thereby causing the flame to be extinguished. The plates are placed closed together and are of considerable area to increase the efiectiveness. The arrangement is diflicult to clean and has a high air resistance.

It is an object of my invention to provide one or more flame proof screens in the form of heat exchangers which have a cooling or condensing eflect on the air used for ventilating or air conditioning a space or spaces which contain, or are interconnected through the ventilating or air conditioning system with other spaces which contain, an inflammable substance or vapor.

A further object is to make such a flame screen in which the resistance of theheat exchangers is very low and the heat exchangers are easily cleaned.

A still further object is to provide means whereby these heat exchangers may be kept at a temperature low enough to condense an inflammable vapor entirely or to cause concentration thereof to be sufliciently'reduced to prevent the possibility of an explosion or burning as a result of a spark (of either a static or electrical apparatus source).

A still further obiect is to construct a blower assembly for insertion in a ventilating or air or spaces which contain an inflammable substance or vapor;

Fig. 2 shows a. diagrammatic view of a fan or fan and motor used for recirculating air in a space or spaces either or both or which contain an inflammable substance or vapor;

conditioning duct adapted to furnish the circulating pressure therein and at the same time to prevent the passage of an inflammable vapor or a flame either to or from said assembly.

A further object is to make a cooling plate or tube coil more adaptable to various air or other gas circulating systems, especially in close quarters, as on shipboard, by making it in 'two or more smaller parts instead of a single large unit.

Other and more specific objects of my invention will become apparent as the description thereof proceeds, reference being had to the accompanying drawings, wherein:

Fig. 1 shows a diagrammatic view of a fanoperated ventilating systemwithin which heat exchanger screens have been installed in the ducts supplying air to or exhausting air from a space Figs. 3 and 4 show screen; and

Figs. 5 and 6 are plan and side views, respectively, of a modified arrangement of my'flame proof screens in a cross connection having two inlet and two outlet ducts.

Similar parts in the several arrangements are designated by the same numerals. There is shown at 4a fan driven by a motor or other source of power I and enclosed by casing 5 to form a plenum space 3. In Fig. 1, heat exchangers l. are installed in branch ducts l2, to or from spaces containing inflammable substance or vapor, whichare connected to the plenum space 3 by transition piece or duct 6 at flange or joint I Heat exchangers i are connected to the outer ends ofthe transition pieces 6 and ducts l2 are connected to the outer ends of the heat exchangers l In Figs. 3 and a, ducts 8 are connected to the outer ends of the heat exchangers. 20 represents a con-- a detail of a fan and a ventional temperature controlling device. It also.

for the space or spaces served which may containan inflammable substance or vapor.

Air being supplied to or exhausted from the space or spaces must pass through the heat exchangers which have a condensing and cooling effect on the air to prevent Jame propagation or an explosive or burning mixture from coming in contact with the fan or a fan and motor.

The arrangement of the system and various parts shown in Fig. 2 are similar to those in Fig. 1, except that the system is used to recirculate air within a'spac'e or spaces, either or both of which contain an inflammable substance or vapor. The

air discharges from the system through outletsl3 and is returned to the system through inlets l4.

-Air entering or being discharged from the system must pass through the heat exhangers. which have a condensing and cooling effect on the The condensing effect prevents any ex-v air. plosive or burning mixture from coming in contact with the fan or a fan and motor from which a spark (static or electrical) may occur. The cooling effect prevents a flame which may result from a spark or short circuit within the motor from passing beyond the heat exchangers in either direction, or prevents a flame as a result of burning within one space topass through the duct system into another space.

Figs. 3 and 4 show a detailed arrangement of a pair of heat exchanger screens. The lettering is similar to that in Figs. 1 and 2. In addition to parts designated in Figs. 1 and 2, there'are shown at connections for circulating a cooling medium by gravity or mechanical means. The cooling medium circulates through tubes 9 on which are fins 2. In this arrangement as in all the others shown, the total cooling or condensing surface, instead of being concentrated in a single casing or housing, is divided into two or more heat ex changer screens in separate casings or housings with the fan and motor or other air mover or blower interposed between the screens, so that two such screens with the fan and motor between are always in series in the air stream regardless of the'direction of circulation of the air or gas in the system or the direction in which the potential flame might tend to propagate. This arrangement not only provides protection for the fan and motor but provides a means for arranging the parts to simplify the installation without changing the performance characteristics of the system. Furthermore the same cooling effect may be obtained in the system with the possibility of a more suitable arrangement of parts where the installation has to be made in limited quarters.

Figs. 5 and'6 show a variation of Figs. 3 and 4 and are similarly lettered to indicate similar parts. The casing 5" provides a cross-shaped connector uni-t whose four openings are joined, respectively, to the four openings in the cross-shaped conduit combination provided by the four conduits 8". Drip pans are shown as a means of collecting condensate, and the arrows 16 indicate one possibility of the intended direction of airflow. The flow may, however, be in the opposite direction depending on the arrangement of the fan blade pitch. The condensate may be drained by means of the drainage'pipes ll". The tubes 9"" may open at each side of the conduit into headers or their ends may be connected in pairs at eachside so as to form a continuous coil in a plane normal to theduct as shown in the drawings. These tubes may have fins, 'as shown for increasing the surface contact for better heat exchange. Goldwater or other cooling fluid maybe passed through these coils.

The advantage of passing the cooling medium through tubes in the cooling unit instead of spraying water in curtains or over screens as in some known circulating systemais that there is no contamination of the condensate in cases where it is recoveredfor useful purposes from the pans shown in Figs. 5 and 6.

The advantages of having a common fan driving unit for two opposed openings in a blower casing, are that it furnishes a construction that may more readily be combined in a compact installation and in certain restricted compartments where only limited spaces are available, as is often the case on board ship. The arrangement shown in Figs. 5 and 6 is particularlyadapted for a central location between'a series-of compartments to eachof which a branch supply and exhaust conduit from one of the corresponding ducts 8" is connec'ted for. supplying the necessary circulation therein.

The invention described herein may be manufactured and used by or for the Government of r the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Having thus set forth anddisclosed the nature of this invention, I claim: I 1 1. Means for preventing fire in a gas duct having'a section with potentially spark producing apparatus therein and potentially combustible gases flowing therethrough, comprising means for defining said section, including cooling coils at both ends thereof having a cooling medium commonly fed thereto and commonly controlled from a single stage compressor means, and means for reducing'the temperature of said cooling medium sufficiently to condense any combustible vapors in said gases whereby to render said gases nonflammable by accidental sparks.

2. In a ventilating conduit combination having potentially spark producing equipment therein, comprising an electrical motor driven fan positioned in one duct of said conduit combination, heat exchangers provided with cooling coils positioned one'on' each side of the electricalmotor driven fan in said duct, said cooling coils provided therein with a circulating, refrigerant fluid and of sufiicient refrigerating capacity to cause said heat exchangers to function as a flame-proof screen to prevent any flame propagation in said combination out of said duct between said coils from said potentially spark producing equipment.

3. In an air conditioning conduit combination provided with ducts, a duct section provided with thereof, said cooling coils being provided with a circulating, reirigerating'fluid' and of sufficient thermal capacity 'to function as a flame-proof screen iniaddition to functioning. as an air conditioning means.

4. A gas circulation cross-shaped conduit combination provided with two oppositely disposed inlet openings and two oppositely disposed outlet openings, a cross-shaped connector unit 0 ecti'ng said conduit combina openings, said connector un' a potentially spark producin side of the centerthereof in "two of its oppositely disposed openings which are connected to the correspondingly located openings of the cross shaped conduit combination, and a cooling coil, providedwith a circulating," refrigerating fluid,

the conduit combination and the connector unit,

of sufiicient thermal-capacity to serve as a flame quenchingmeans for confining any flame that might occur within said connector unit.

' r JOHN W. FORD.

' REFERENCES CITED The following references are of record in the flle'of this patent! 7 v UNITED STATES PATENTS" J 7 Number Cornell Dec. 20. 1938 met and outlet positioned at each of the four openingsbetween 

